Abstract: Ultraold Rydberg gases are a promising system for exploring many ideas in the area of quantum computation, quantum optics, novel states of matter, and many-body physics. A key to understanding ultracold Rydberg gases and making progress in these exciting directions is to understand how Rydberg atoms interact with other atoms. We will review our understanding of Rydberg interactions including the effect of external fields. We will focus on describing interactions that lead to 2 types of novel molecule formation, so called 'trilobite' molecules and macrodimers. We have recently observed 'trilobite' molecules in an ultracold Cs gas and found that these molecules possess dipole moments in excess of 30D. In prior work, we detected electric field tunable Cs macrodimer molecules, molecules with bond lengths of ~5 microns. In this talk, we will compare and contrast these exotic forms of matter as well as try to place their study in the context of understanding Rydberg atom interactions quantitatively.

Abstract: Agricultural production and processing represent diverse, independently managed and complex systems overlaid with equally if not more complex biological and climactic variables. As such, waste happens, but not necessarily where one might expect. According to Jonathan Bloom in American Wasteland, per capita food waste has increased by 50% since 1974, with the majority of this waste in the trash bin at home. Food currently accounts for 19% of landfill waste. Additionally, food production represents almost one fifth of total U.S. energy use and the vast majority of consumptive water use. Meanwhile, over 20% of children are in food insecure households aEuro" meaning that they are unsure of where their next meal will come from. Hunger in the U.S. is at the highest level since recording of such data began and continues to rise. In this seminar, we will discuss the complexities of the food system that lead to waste and potential solutions that address hunger while protecting the environment.

Abstract: In one extreme, where the interactions are sufficiently weak compared to the interactions, electrons form a "Fermi liquid" - the state that accounts for the properties of simple metals. In the other extreme, where the interactions are dominant, the electrons form various "Mott" insulating or "Wigner crystalline" phases, often characterized by broken spatial and/or magnetic symmetries. Corresponding charge and/or magnetically ordered insulating phases are common in nature. Between these two extremes lie highly correlated electronic fluids, and correspondingly a host of interesting and perplexing materials, including such diverse systems as the cuprate and iron-based high temperature superconductors, the failed metamagnet Sr3Ru2O7, and a variety of quantum Hall fluids. Some insight into this rich intermediate coupling regime can be obtained from viewing it as a partially melted electron solid, rather than as a strongly interacting gas. Here, analogies with the liquid crystalline phases of complex classical fluids provide useful guidance for a new approach to this key problem in condensed matter physics.

Abstract: In 1928 Dirac reconciled quantum mechanics and special relativity in a set of coupled equations which became the cornerstone of quantum mechanics. Its main prediction that every elementary particle has a complex conjugate counterpart - an antiparticle - has been confirmed by numerous experiments. A decade later Majorana showed that Dirac's equation for spin-1/2 particles can be modified to permit real wavefunctions. The complex conjugate of a real number is the number itself, which means that such particles are their own antiparticles. The most intriguing feature of Majorana particles is that in low dimensions they obey non-Abelian statistics and can be used to realize quantum gates that are topologically protected from local sources of decoherence. While the search for Majorana fermions among elementary particles is still ongoing, excitations sharing their properties may emerge in electronic systems. It has been predicted that Majorana excitations may be formed in some unconventional states of matter. I will report the observation of the fractional ac Josephson effect in a hybrid semiconductor/superconductor InSb/Nb nanowire junction, a hallmark of topological matter. When the junction is irradiated with rf frequency f at zero external magnetic field, quantized voltage steps (Shapiro steps) with a height hf/2e are observed, as is expected for conventional superconductor junctions where the supercurrent is carried by charge-2e Cooper pairs. At high fields the height of the first Shapiro step is doubled to hf/e, suggesting that the supercurrent is carried by charge-e quasiparticles. This is a unique signature of Majorana fermions, elusive particles predicted ca. 80 years ago.

Abstract: Please visit the following link for more details:http://cmb.physics.wisc.edu/journal/index.html
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (lzhang263@wisc.edu)

Abstract: To date the approach to MHD control has largely been dependent on incorporation of the well known MHD models to provide the predictive capability required for synthesis of real-time, closed-loop active control algorithms. Through the use of system identification techniques Erik Olofsson has shown that it is possible to model magnetohydrodynamic stability based on unprejudiced empirical data derived from experimental observation (i.e. no MHD equations in the derived magnetohydrodynamic stability model). The ambition has been to approach experimental modal analysis in a generic manner without invoking prior MHD model knowledge. As stated in the thesis, using EXTRAP T2R data it has been possible to iteratively develop and reality-check both dynamical systems estimation/identification and control synthesis techniques.